Persistence of the invasive bird-parasitic fly Philornis downsi over the host interbreeding period in the Galapagos Islands

Mariana Bulgarella, M. Piedad Lincango, Paola F. Lahuatte, Jonathan D. Oliver, Andrea Cahuana, Ismael E. Ramírez, Roxanne Sage, Alyssa J. Colwitz, Deborah A. Freund, James R. Miksanek, Roger D. Moon, Charlotte E. Causton, George E. Heimpel

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Many parasites of seasonally available hosts must persist through times of the year when hosts are unavailable. In tropical environments, host availability is often linked to rainfall, and adaptations of parasites to dry periods remain understudied. The bird-parasitic fly Philornis downsi has invaded the Galapagos Islands and is causing high mortality of Darwin’s finches and other bird species, and the mechanisms by which it was able to invade the islands are of great interest to conservationists. In the dry lowlands, this fly persists over a seven-month cool season when availability of hosts is very limited. We tested the hypothesis that adult flies could survive from one bird-breeding season until the next by using a pterin-based age-grading method to estimate the age of P. downsi captured during and between bird-breeding seasons. This study showed that significantly older flies were present towards the end of the cool season, with ~ 5% of captured females exhibiting estimated ages greater than seven months. However, younger flies also occurred during the cool season suggesting that some fly reproduction occurs when host availability is low. We discuss the possible ecological mechanisms that could allow for such a mixed strategy.

Original languageEnglish (US)
Article number2325
JournalScientific reports
Issue number1
StatePublished - Dec 2022

Bibliographical note

Funding Information:
This work was funded by Grants from Galapagos Conservancy, International Community Foundation (with a Grant awarded by The Leona M. and Harry B. Helmsley Charitable Trust) and from Lindblad Expeditions-National Geographic Fund.

Funding Information:
We thank Drs Tim Kurtti and Ulrike Munderloh for allowing use of their equipment for this study. Johanna Casta?eda, Xavier Pilataxi, Nicholas Heimpel, and Arno Cimadom helped with fly collection and processing. We also thank Birgit Fessl for comments on the manuscript and Christian Sevilla for support in making this Project possible. Dr Adri?n Di Giacomo provided information on the Chaco region of Argentina. We also thank Prof Sonia Kleindorfer and an anonymous reviewer for their thoughtful comments. Permission to conduct this study was granted by the Galapagos National Park Directorate (Project: PC-02-14, PC-10-15, & PC-18-16: Control of the Invasive Parasite, Philornis downsi and its Impact on Biodiversity). This is contribution number 2327 of the Charles Darwin Foundation for the Galapagos Islands.

Publisher Copyright:
© 2022, The Author(s).

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't


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